The present invention relates to a multiplexed optical port for electric metering equipment. In particular, the invention relates to an optical port multiplexer for an electric meter of the type which uses a glass cover.
Commonly used electric meters and registers make use of cases which typically include a glass (or other transparent) cover. Such equipment can include, within the cover, a variety of options, such as the ability to meter a variety of parameters over different time periods. In the past, a variety of means have been used to "read" electric meters. Such means included having a meter reader actually read numbers off mechanical dials located within the glass cover. Newer, solid-state meters typically have liquid crystal displays (LCDs) which can be visually read by a meter reader. Alternatively, a number of solid state meters make use of an optical port which can be used to read the contents of registers within the meter by means of a hand held unit called a "retriever/programmer", which unit can also be used to program the various functions within the solid state meter.
In a number of situations, it is desirable to add additional features to an existing meter which already has an optical port. For example, it may be desirable to add a recorder feature, which is capable of recording pulses verses time, to an existing register, of the type which normally does not have such a feature. In order to avoid having to redesign the cover and add an additional optical port, it would be desirable to be able to multiplex a single optical port. However, such multiplexing normally requires some means for seIecting the system, internal to the meter, with which the optical port is to be used.
The problem which presents itself involves the question of how to multiplex the optical port without having to change the mechanical design of the meter cover in order to permit retrofitting additional features relatively easily, i.e., without major mechanical modifications. Thus, a first concern involves avoiding the addition of an external switch or additional optical ports. This could be accomplished by using a "master/slave configuration", in which one of the systems performs the task of multiplexing the data lines by means of an internal processor. Alternatively, it could be accomplished by using a microprocessor based intelligent gateway. Either of these approaches would respond to signals provided through a single optical port by the external retriever, but both would require substantial cost in circuitry internal to the meter. In addition, it would require changes in the firmware of both the meter systems and the external retriever. Accordingly, a second, equally important problem, involves the question of how to multiplex a single optical port without having to change the electrical design or the firmware of the meter or the retriever.